Novel halo- and thermo-tolerant Cohnella sp. A01 L-glutaminase: heterologous expression and biochemical characterization

Abstract

L-glutaminase importance to use in the food industry and medicine has attracted much attention. Enzymes stability has always been a challenge while working with them. We heterologously expressed and characterized a novel stable L-glutaminase from an extremophile bacterium (Cohnella sp. A01, PTCC No: 1921). Km, Vmax, catalytic efficiency and specific activity of rSAM were respectively 1.8 mM, 49 µmol/min, 1851 1/(S.mM) and 9.2 IU/mg. Activation energy for substrate to product conversion and irreversible thermo-inactivation were respectively 4 kJ/mol and 105 kJ/mol from the linear Arrhenius plot. rSAM had the highest activity at temperature 50 °C, pH 8 and was resistant to a wide range of temperature and pH. In compare to the other characterized glutaminases, rSAM was the most resistant to NaCl. Mg2+, glycerol, DTT, and BME enhanced the enzyme activity and iodoacetate and iodoacetamide inhibited it. rSAM had only been partially digested by some proteases. According to the Fluorimetry and Circular dichroism analysis, rSAM in pH range from 4 to 11 and temperatures up to 60 °C had structural stability. A cysteine residue in the enzyme active site and a thiol bond were predicted upon the modeled tertiary structure of rSAM. Present structural studies also confirmed the presence of a thiol bond in its structure.